you can use tools from your neighbor as long as he or she is not a machine shop.
I can loan (not rent, as that would not be legal) my Jigs, I just can not do the work for you at all.
I can point and advise I just can not touch at all.
This is the way the law reads as I do not use these things to make a Living like a machine shop or gun store (if I did then not legal).
The ATF laws change all the time and I keep reading the new ones as they come down and if I am sketchy on any I write the ATF myself and get Clarity on them.
I have not had or seen any new laws in a while so all should be good.
Build parties should not be allowed in CNC shops but if two or three buddies got together at ones house and used hand tools that one had all good as long as each one Builds and finishes their own with no help other than Questions and answerers and pointing (kind of like watching a YouTube video and doing the steps while watching the video, this his how one ATF agent explained it to me).
Now you guys interpret the ATF rules the way you see it and if it differs from mine still all good.
(edit) I would like to add that if you are not comfortable with Building your own and not sure of the laws then just do not do it, Simple answer.
I Serial each one I build so I do not have to explain to an officer why I have a rifle with no serial number (perfectly legal BTW, I keep a copy of the ATF rules with me Just in case before I started Serializing all of my lowers) but I have never been asked yet so not an issue yet.